There is many people who have Thyroid issues who use a combo and many of them report that it has helped them tremendously compared to use using T4.
Many doctors shoot for a healthy range of 16:1 T4:T3, which reflects roughly how much your the body makes on average naturally when healthy (100mcg T4 and 6mcg T3).
If your buddy has T3 in usual pill form, just take a quarter of a regular pill and he should have enough.