SYRACUSE — An upstate New York family doctor has admitted writing prescriptions to his patients for thousands of pills in exchange for some of the drugs, federal prosecutors said.

Dr. Harry Black, 62, and his wife Lisa Black, 44, have pleaded guilty to conspiring to obtain prescription drugs by fraud or subterfuge, an assistant U.S. Attorney, John Katko, said. The plea was announced yesterday and will be entered in U.S. District Court on Aug. 19.

Black and his wife — along with 15 other co-defendants — face up to 20 years in federal prison. Black also faces losing his $400,000 home, his $110,000 office and his medical license.

All but one of the other accused conspirators have pleaded guilty.

An attorney, William Sullivan, who represented the Blacks, said his clients pleaded guilty after six months of negotiations. Mr. Katko said the government made it clear it wouldn’t reduce charges in exchange for a plea.

“(Dr. Black) was at the center of the conspiracy,” Mr. Katko said. “His charges should reflect that.”

The Blacks and the others were charged in early June 2007. Authorities raided Black’s house and found hundreds of amphetamine capsules, plastic bags with cocaine residue, unmarked pill bottles containing OxyContin, marijuana, and prescription bottles bearing the names of many other people. Agents also found two handguns.

Prosecutors said Black would fill out large prescriptions for drugs such as Oxycontin, Vicodin, and amphetamines and his wife and patients would give him some of the drugs. The group would shop at different pharmacies to hide their trail and pay cash to avoid insurance company regulations, prosecutors said.

Black was previously censured and put on probation by the state Department of Health for five years starting in 1998 for inappropriately prescribing drugs to his wife.