Pick any list of the most influential inventions in history and somewhere on it you will find drugs. Aspirin, Penicillin, Insulin — these are not just medicines, they are technologies that fundamentally changed what it meant to be sick and what doctors could do about it. This article walks through ten drugs that, in our view, did the most to shape modern medicine, with a short explanation of how each one works and why it matters.
You can explore many of these molecules interactively in the Drug Discovery Lab. Pull up the structure, calculate properties, run analogs, and see what makes each one work at the chemistry level.
1. Aspirin (1897) — the original NSAID
Felix Hoffmann at Bayer first synthesized acetylsalicylic acid in 1897 by acetylating salicylic acid, a compound long known from willow bark. The acetylation made it gentler on the stomach and easier to swallow, and Bayer launched it as Aspirin in 1899.
It took almost eighty years to figure out how it actually works. John Vane showed in 1971 that aspirin acetylates serine 530 of cyclooxygenase (COX), permanently blocking prostaglandin synthesis. That single mechanism explains aspirin's effects on pain, fever, inflammation, and platelet aggregation. Aspirin is still one of the most-consumed drugs in the world and is one of the few drugs that earned its discoverer a Nobel Prize after the fact.
2. Penicillin (1928 / 1941) — the antibiotic era begins
Alexander Fleming famously came back from a holiday in 1928 to find that a Petri dish of Staphylococcus had been contaminated by a Penicillium mold, and that the bacteria had died in a halo around the mold. He published the observation but didn't manage to purify the active compound. That happened more than a decade later, when Howard Florey, Ernst Chain, and Norman Heatley at Oxford figured out how to produce penicillin in usable quantities, just in time for World War II.
Penicillin is a beta-lactam: it irreversibly inhibits the transpeptidase enzymes that crosslink bacterial peptidoglycan cell walls. Without crosslinking, the cell wall fails under osmotic pressure and the bacterium lyses. Penicillin opened the antibiotic era and made surgery, chemotherapy, transplants, and modern intensive care medically thinkable for the first time.
3. Insulin (1921) — diabetes from death sentence to chronic disease
Before 1921, type 1 diabetes was a slow death sentence — children with the disease typically died within a year. Frederick Banting and Charles Best, working in Toronto with John Macleod and James Collip, isolated insulin from dog pancreas, then from cow and pig pancreas, and showed that injecting it could reverse the dying process in diabetic children. The first human patient, Leonard Thompson, was treated in January 1922.
Insulin is a small peptide hormone (51 amino acids in two chains connected by disulfide bonds) that signals through the insulin receptor to drive glucose uptake into cells. Modern insulin therapy uses recombinant human insulin and engineered analogs like Lispro, Aspart, and Glargine that have different pharmacokinetic profiles. Diabetes is now a chronic, manageable condition for hundreds of millions of people worldwide.
4. Chlorpromazine (1952) — the start of modern psychiatry
Chlorpromazine (Thorazine) emerged from antihistamine research at Rhône-Poulenc in 1950. French surgeon Henri Laborit noticed that it produced a remarkable calming effect in surgical patients without putting them to sleep, and psychiatrists Jean Delay and Pierre Deniker tested it on patients with schizophrenia. The results — a sharp reduction in hallucinations, agitation, and delusions — were unlike anything that had been seen before.
Chlorpromazine works by blocking dopamine D2 receptors in the mesolimbic pathway, an insight that took years to formalize and eventually led to the dopamine hypothesis of schizophrenia. Its introduction effectively emptied state mental hospitals across the developed world over the following two decades and established psychopharmacology as a real branch of medicine.
5. Warfarin (1948) — from rat poison to lifesaver
In the 1920s, cattle in the upper Midwest started dying of uncontrolled bleeding after eating spoiled sweet clover hay. Karl Link at the University of Wisconsin identified the responsible compound — dicoumarol — and his lab eventually synthesized a more potent analog called warfarin (Wisconsin Alumni Research Foundation + coumarin). Warfarin was first marketed as rat poison in 1948.
It became a human medicine almost by accident, after a US Army inductee survived a warfarin suicide attempt. Doctors realized the dose-response could be controlled. Warfarin works by inhibiting vitamin K epoxide reductase (VKORC1), which is required to recycle vitamin K for the activation of clotting factors II, VII, IX, and X. It became the standard anticoagulant for stroke prevention in atrial fibrillation and for venous thromboembolism, and remains widely used despite the rise of newer DOACs.
6. Diazepam (1963) — the benzodiazepine revolution
Leo Sternbach at Hoffmann-La Roche discovered chlordiazepoxide (Librium) in 1957, more or less by accident, and followed up with diazepam (Valium) in 1963. Benzodiazepines bind a specific site on the GABA-A receptor and potentiate the effect of the inhibitory neurotransmitter GABA, producing anxiolytic, sedative, and muscle-relaxant effects with a much wider safety margin than the barbiturates that they replaced.
At their peak in the 1970s, Valium was the most-prescribed drug in the United States. The benzodiazepine era taught medicine important lessons about tolerance, dependence, and withdrawal that still inform how we use sedative-hypnotic drugs today.
7. Cimetidine (1976) — the first rationally designed blockbuster
James Black at Smith Kline & French set out in the 1960s to design a histamine receptor antagonist for stomach acid secretion. The known H1 antagonists didn't work, so Black's team hypothesized a separate “H2” receptor and deliberately designed compounds against it, starting from the histamine scaffold and methodically modifying it. The result was Cimetidine (Tagamet), launched in 1976. It became the first billion-dollar drug.
Cimetidine is important not just because it transformed peptic ulcer disease — which had been a major source of morbidity and surgical interventions — but because it proved that you could rationally design a drug against a specific receptor by modifying the natural ligand. James Black went on to do the same thing with beta-blockers (Propranolol) and shared the 1988 Nobel Prize.
8. Fluoxetine (1987) — the SSRI revolution
Fluoxetine (Prozac) was developed at Eli Lilly through a rational program targeting the serotonin reuptake transporter. Approved in 1987, it was the first selective serotonin reuptake inhibitor (SSRI) to reach widespread clinical use. Compared to the older tricyclics and MAO inhibitors, SSRIs had a vastly improved safety profile, far fewer drug interactions, and were less dangerous in overdose.
The clinical and cultural impact was enormous. Depression was suddenly a treatable condition that primary care doctors could manage, not a specialist-only diagnosis. The SSRI class (Sertraline, Paroxetine, Citalopram, Escitalopram) is now among the most-prescribed drug classes in the world. The mechanism — blockade of the SERT serotonin transporter — is well established, even though the broader question of how that produces antidepressant effects is still debated.
9. Imatinib (2001) — the targeted therapy revolution
Chronic myeloid leukemia (CML) is caused by a specific chromosomal translocation that fuses the BCR and ABL genes, creating a constitutively active BCR-ABL tyrosine kinase that drives uncontrolled cell proliferation. In the 1990s, scientists at Ciba-Geigy (later Novartis), led by Brian Druker, Nicholas Lydon, and Jürg Zimmermann, designed a small molecule that fit into the ATP-binding pocket of BCR-ABL and shut it off. That molecule was Imatinib (Gleevec).
Approved in 2001, Imatinib turned CML from a fatal disease with a median survival of three to five years into a chronic condition with near-normal life expectancy when patients stay on therapy. It was the first proof-of-concept for targeted kinase inhibitors and launched the era of precision oncology. Dozens of kinase inhibitors have followed for many other cancers.
10. Semaglutide (2017) — the GLP-1 era
GLP-1 agonists are not the first drugs for type 2 diabetes — metformin held that title for decades — but Semaglutide (Ozempic, Wegovy) and Tirzepatide (Mounjaro, Zepbound) have produced something unprecedented: significant, sustained, injectable weight loss that approaches the effect of bariatric surgery. They've changed the conversation about obesity in a way no previous medicine ever did.
Semaglutide is a long-acting analog of the incretin hormone GLP-1, modified with a fatty acid chain that lets it bind to serum albumin and circulate for days. It activates the GLP-1 receptor on pancreatic beta cells (improving glucose-dependent insulin secretion), in the gut (slowing gastric emptying), and in the brain (suppressing appetite). The combined effect is better glucose control and substantial weight loss. We dive deeper into the GLP-1 story in our companion post on GLP-1 agonists.
What you can do in the Drug Discovery Lab
The Drug Discovery Lab has individual workspaces for many of the drugs in this article:
Each workspace lets you see the structure, calculate Lipinski properties, view the SMILES, and run analogs. For drugs that are also peptides (insulin, semaglutide), the Peptide Lab adds sequence-level analysis.
Bottom line
Drugs that change history have a few things in common. They usually solve a problem people had given up on. They often teach us something new about basic biology in the process. And they almost always start as a single observation or hypothesis that someone took seriously enough to chase down. From willow bark to GLP-1 fatty acid conjugates, the through-line is the same: deep understanding of one mechanism, applied relentlessly, can move medicine in a way nothing else can.