So i thought i'd create a thread regarding this. For those who don't know, OTC stands for 'over the counter', meaning you don't need a prescription to obtain them. Most pharmaceutical antiemetics are also antihistamines, which are antiallergy medicines, they slow down histamine release.

Natural:
Ginger - is supposed to be very effective, even more effective than placebo i've read.
Cannabis - Controversial, but it's supposed to be effective as well. It may not be for everyone, some may not be able to obtain this legally and some may be completely against drug use. But nonetheless, it's a natural antiemetic and a good all-around medicine.
Pepper/spearmint

These are just 3 common ones out of many, many available.

OTC:
Cyclizine
Meclizine
Diphenhydramine
Dimenhydrinate

There oughta be more out there, but these are fairly common.
These are just the active substances, i don't wanna use brand names 'cause they can vary depending on where you live. Some of these might only be available with a prescription, or maybe not at all, in your country. Cyclizine and diphenhydrinate are not available where i live, but seem to be just about everywhere else. There could possibly be a non-prescription strength and also a prescription strength where you live, so look that up beforehand if you decide to try either one of these. Since all of these are antihistamines, and usually, OTC antihistamines with antiemetic properties are mainly for the antihistaminic effects, you might wanna do a quick google search to find out if the dosage you're able to get is strong enough for its antiemetic properties, which it generally should. Just thought i should note that.

Prescription:
Promethazine
Alimemazine (fairly uncommon in loads/most countries, however, fairly common in mine.)
Mirtazapine (i'm not 100% sure with this one, it's most commonly prescribed as an anti-depressant and/or for its hypnotic effects, but i've read on some websites that it's supposed to have antiemetic properties. I've also read that it can potentiate CNS-depressants, such as alcohol, benzos, opiates/opioids and barbiturates, so if you're prescribed any of these type of depressants, be aware of this and ask your doctor before, and do your own research as well. Generally low doses should be okay, but everyone's bodies work differently, so always ask your doctor first!)
Ondansetron (primarily used for its antiemetic properties. Not very effective against motion sickness though)
Hydroxyzine

These are just a few out of a LOT out there. Some might be OTC where you live, some may not even be available.

I hope this helped!