How long is my medical marijuana card good for in Ohio?

Generally speaking: Your Ohio medical marijuana card is good for one year, except in the case of terminally ill patients.

Here is the full answer from the Ohio MMCP website:

A patient or caregiver registration will be valid from the date of issuance and expire one year later, on the last day of the month it was issued. If the patient is diagnosed as terminally ill, the patient’s registration will expire after six months.