How long can you take thalomide?

Did you mean thalidomide?

This is the FDA dosage information from http://www.drugs.com/ppa/thalidomide.html
(Note: there is no maximum treatment time)

"... ENL (erythema nodosum leprosum)
Adults
PO Initial dose 100 to 300 mg per day, preferably 1 h after the evening meal. Give 400 mg per day at bedtime or in divided doses at least 1 h after meals to patients with severe cutaneous ENL reaction or to those who have previously required higher doses to control reaction.

Tapering Schedule
Continue dosing until signs and symptoms have subsided, usually for at least 2 wk. Taper in 50 mg decrements every 2 to 4 wk. In patients requiring prolonged maintenance treatment to prevent recurrence or who flare during tapering, decrease medication every 3 to 6 mo in decrements of 50 mg every 2 to 4 wk.

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Multiple Myeloma
Adults
PO 200 mg once daily, preferably at bedtime and at least 1 h after the evening meal. Dexamethasone 40 mg is administered on days 1 to 4, 9 to 12, and 17 to 20 every 28 days."