MUSKEGON, Mich. (WOOD) — Two men accused of drugging and raping more than two dozen women are facing more serious charges.

Monday, prosecutors upgraded the charges against 31-year-old Larry Stiff and 34-year-old Joshua Humphrey to first-degree criminal sexual conduct, according to Muskegon County court records obtained by 24 Hour News 8.

Stiff and Humphrey were previously charged with third-degree criminal sexual conduct for an incident in February.

Each suspect also faces two counts of first-degree criminal sexual conduct in a second case from Oct. 31, 2013. Those charges were filed earlier this year.

The men are accused of assaulting women who they met online, in bars or even at high school events.

While investigators believe there are at least 25 victims, women who say they were assaulted by the pair believe there are many more.

Some victims testified that one of the men would buy them a drink. Later, they woke up unclothed after being sexually assaulted.

At least two of the women reported becoming dizzy and disoriented. Some can vaguely remember being assaulted. Others say they have no memory of what happened.

Police affidavits show Humphrey had been prescribed tramadol, a narcotic used to treat pain. Investigators discovered that the prescription had been refilled more than 20 times over a six-month period last year.

Both Stiff and Humphrey face life in prison if convicted.

Potential victims or anyone with information about the men can contact Muskegon police at 231.846.8477 or Silent Observer at 231.722.7453.