It's Henderson's second such suspension this season; he'd been suspended for four games earlier in the year. He has already appealed the suspension and had the ruling upheld.
On the surface, this isn't unusual. Players get suspended for violating the substance abuse policy all the time, and many of them are suspended for using Henderson's substance of choice: marijuana.
What makes this situation different is that Henderson was prescribed medicinal marijuana to treat his Crohn's disease, a chronic inflammatory bowel disease that affects the lining of the digestive tract.
Henderson uses marijuana to treat the pain from the disease and two intestinal surgeries he has undergone as a result of it. Henderson's agent, Brian Fettner stated at the time of Henderson's first surgery, "There is zero allowable medical exemption for this per the NFL; however, there clearly should be."
NFL.com reported in the wake of the second suspension that Henderson, "needs cannabis. You can't take pain killers with the way his intestines are." Per the same report, Henderson is considering litigation in order to find a way back on the field. He would obviously not be the first player to pursue litigation against the NFL. Several players have done so over the last few years, though most of those players have been challenging the league's personal conduct policy and not the substance abuse policy.