便秘薬って英語でなんて言うの？

Laxatives' are the medicine you used to help when you have constipation ( difficulty in going to the toilet)
So you would say 'Could i get some laxatives for my constipation'
An example of laxatives is - 'Senokot'

Medicine that is used to help constipation is a laxative.
"Spicy curry is a natural laxative"

Laxatives are medicines that help constipation as the intention for taking them is loosen your stools. Stools are a formal word for 'poop'. Many people suffer from constipation and often take laxatives. Other people however, take laxatives believing that it has a purifying effect on their body. In this case, taking laxatives often may cause diarrhoea.

Example:
Yusuke: Hey John, do you want to watch the game at the sports bar tonight?
John: Hey man, I can't. I'm taking laxatives tonight.

Medicine that is usually used to loosen a constipated stomach is called a "laxative". You may use this word in the following ways:
-I need to go to the pharmacy to get a laxative. I have been constipated for a few days now.

A stool softener is type of treatment that makes the stool softer so that it can pass through the lower intestine more easily. A laxative, however, forces the stool out more quickly and can even cause diarrhea. The two medicines are not exactly the same but both can help with constipation. Milk of magnesia is a substance that has a laxative effect and helps with constipation.

Purgative
This is a medicine or natural remedy which is taken to help lessen the difficulty of passing faeces.