I've been on 2 10 day Vipassana meditation retreats (as taught by SN Goenka).

I had bad OCD that was entirely cured after 2 10-day courses + an average of 2-3 hours of meditation practice every day for 1-2 years.

However, even 2 hours of meditation practice for 6 months after the first retreat got my OCD to a very manageable level.

Really recommend going!