Is inh safe?

As safe as many drug. Inh is one of the stalwart drugs with Rifampin in the treatment of active tb. Despite the potential for liver toxicity, it can usually be used under experienced hands in patients with underlying liver diseases either viral or alcoholic.
More or less. It is discouraged to take it after age 35 because the liver toxicity. It also causes peripheral neuropathy ( piridoxine is recommended with it) should be avoided or used with caution in liver disease, or alcoholics.