Physostigmine: What It Is, How It Works, and When to Use It

Physostigmine is a medication that boosts the amount of acetylcholine, a brain chemical that helps nerves talk to each other. By slowing down the breakdown of acetylcholine, it can improve nerve signaling in certain medical conditions.

Doctors mainly give physostigmine for two reasons: to reverse severe anticholinergic poisoning (like an overdose of certain antihistamines or tricyclic antidepressants) and to treat glaucoma by lowering eye pressure. It’s also used in some research settings to study memory and cognition.

How Physostigmine Works

Acetylcholine is broken down by an enzyme called acetylcholinesterase. Physostigmine blocks this enzyme, letting acetylcholine stay active longer. The result is stronger muscle contractions, faster heart rate, and increased secretions (like saliva and sweat). That’s why the drug can reverse the “dry, hot, and confused” symptoms of anticholinergic toxicity.

In the eye, the extra acetylcholine makes the iris muscles tighten, opening the drainage angle and letting fluid flow out. The pressure drops, which helps protect the optic nerve from damage.

Key Benefits and Risks

When used correctly, physostigmine can save a life in poisoning emergencies and help keep glaucoma under control. The dose is usually low – often 0.5 to 2 mg given intravenously in a hospital, or eye drops for glaucoma.

But the drug isn’t without risks. Too much acetylcholine can cause nausea, vomiting, diarrhea, muscle cramps, and even seizures. In people with heart problems, it might trigger irregular beats. That’s why medical staff monitor heart rhythm and breathing during treatment.

Common side effects include sweating, salivation, and blurry vision. Most of these are short‑lived and go away once the dose wears off. If you notice severe cramping, chest pain, or trouble breathing, call a doctor right away.

Because physostigmine crosses the blood‑brain barrier, it can affect thinking and mood. Some patients feel confused or anxious for a short time after the dose. These effects are usually mild and reverse quickly.

Pregnant or nursing women should avoid physostigmine unless a doctor says the benefits outweigh the risks. The drug can pass into breast milk and might affect the baby’s nervous system.

When you get physostigmine, follow these practical tips: take the exact dose prescribed, never mix it with other anticholinergic drugs, and keep a list of any allergies. If you’re using eye drops, wash your hands before and after, and store the bottle in a cool, dry place.

If you’re prescribed oral physostigmine for a rare condition, set a reminder to take it at the same time each day. Skipping doses can cause a rebound of symptoms, especially in glaucoma patients.

Remember, physostigmine is a powerful tool, but it works best under a doctor’s supervision. Don’t try to self‑treat an anticholinergic overdose at home—call emergency services and let professionals handle the medication.

In short, physostigmine helps the body’s own nerve signals do their job, whether that means clearing up a poisoning or lowering eye pressure. Knowing the right dose, watching for side effects, and staying in touch with your healthcare provider keeps the benefits outweighing the risks.