Why do drugs that do the same thing have different side effects in the same person?
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Pharmacologist here—drugs that have the same “action” may be achieving that result in a different way. Essentially drugs are like keys that interact with locks in your body called receptors. Throughout our body we have many different locks and many copies of each type of lock. When the key binds to the lock, it either makes the lock do what it normally does when interacting with the “natural” key, or it makes it more difficult for the lock to work.
Two sleep drugs:
Diphenhydramine (Benadryl) works by binding a histamine receptor in the brain and preventing the release of more histamine, which acts to promote wakefulness. Effect = drowsiness. There are also histamine receptors in the body and when Benadryl binds these, they promote anti-inflammatory mechanisms, to help with decreasing allergy symptoms
Midazolam (a benzo) works by binding a receptor called a GABA receptor in the brain and when it binds, it causes that receptor to work more—the receptor’s normal job is to decrease activity in neurons. For this reason, benzos can be used to promote sleep, to help with anesthesia and anxiety, but one of their scary side effects is respiratory depression, which happens when neurons supplying the diaphragm (breathing muscle) have their activity decreased too far.
Different locks/receptors have different jobs in the body.
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