Delusions after mistaking one drug for another with a similar name

[kdorian]

Setting: Mars, mid to late 2030s (for a The Martian fanfic)

If possible, I need my character to mistake one drug he needs to take (and is not familiar with) with another drug with a similar name that ends up giving him delusions for a short time. (He's going to think he's a cat. Don't ask.)

Caveats:

• He's trying to be careful, so the drugs need to be reasonably close in spelling, at least enough for a layman to mix them up. He doesn't know how to pronounce them, so that doesn't matter.
• Both drugs need to ones that a group of astronauts spending a month on Mars could conceivably need.
• The drug he's trying to take needs to be a fix for something fairly obviously wrong with him. It does not matter how serious the medical issue is, so long as taking the wrong drug won't leave him dead or disabled, so anything from treating an upset stomach to something he'd need to take after performing surgery on himself will work for story purposes.
• It is not a drug for a chronic condition, simply because there won't be a long-term supply available. This, unfortunately, seems to rule out antidepressants, unless there are any that are used short-term?

While I have found some similarly named drugs where one can cause delusions, I haven't found one with a 'partner' that he would need and might be available. (He doesn't have Parkinson's or HIV, isn't trying to induce ovulation, isn't trying to treat a mental illness, etc.)

Search terms used:
1) Drugs that cause delusions, prescription drugs that cause delusions, drug side effect delusions
2) Similar drug names, confused drug names, similar drug names, drug names that look alike
...Followed by cross-checking until my eyes wanted to bleed.