Sometimes, the weight of evidence on each side is balanced so closely that it's barely possible to see the arms of the scale move. That's the case in the long debate between advocates of a prescription monitoring to prevent fatal drug overdoses and guardians of privacy.

Such programs electronically record every prescription written for certain classes of drugs. Doctors, public health officials and law enforcement agencies that secure a warrant can see how often a suspected abuser has obtained a prescription for each drug. The idea is to make it difficult for abusers to receive multiple prescriptions for the same drug or similar ones.

The increase in drug overdose deaths in New Hampshire, which at 168 topped the state's 129 traffic deaths last year, is horrifying. But so too is the near certainty that extremely private personal information would eventually wind up in the wrong hands. Until the ability to prevent that from happening is ironclad, lawmakers should not assent to a prescription monitoring program.

Fatal overdoses in New Hampshire have more than doubled in the past decade, thanks in great measure to a dramatic increase in deaths from methadone, a synthetic opioid used to treat severe pain and help wean heroin addicts off that drug. Dr. Tom Andrew, the state's chief medical examiner, says methadone is unusually lethal because when used to induce a high, its effects are slow-acting. Users, believing the drug isn't working, take more.

Some abused drugs are stolen, but most are obtained by filling prescriptions from doctors. Abusers go from doctor to doctor and, since a physician has no way of knowing whether another doctor has just written a prescription for the same drug, get multiple prescriptions. Drug monitoring programs, proponents say, greatly reduce doctor shopping. And they allow doctors, who, when they punch in a security code, see the patient's prescription history, to see when potential harmful or fatal interactions could occur between drugs prescribed by different physicians.

Though more than 30 states have sanctioned the creation of a prescription monitoring system, most are too new to judge their effectiveness. The oldest programs were adopted by Nevada in 1997 and Kentucky in 1999. Studies cited by the National Conference of State Legislatures suggest that the monitoring programs dramatically reduce prescription forgery and doctor shopping, but they also push abusers to states lacking a program and to the internet.

Every New England state but New Hampshire has now approved a monitoring program, so attempts to procure drugs illegally here will likely increase. That means greater vigilance on the part of the local medical community and increased scrutiny by law enforcement will be necessary.

The push for monitoring is coming not just from doctors and public health officials but the attorney general's office. And it would likely be a useful tool. But it's easy to imagine a time when lobbyists could convince lawmakers that the drug problem has become severe enough to grant law enforcement agencies unfettered access to everyone's prescription history without a warrant. Then, agents would view the private medical information of hordes of innocent people in hopes of nabbing a small number of abusers.

Even more troubling is the thought that computer hackers or bribed employees could obtain the records and sell them. The information would be very valuable to pharmaceutical companies, and to insurers and employers who want to avoid both abusers and people in need of expensive health care.

Banks, major retail chains, communications systems and federal agencies including the Department of Veterans Affairs, FEMA, the nation's nuclear laboratories, companies working for the Department of Homeland Security, the CIA and the FBI have all been breached with some degree of success by hackers or had information stolen or lost.

Privacy concerns have trumped the potential value of establishing a prescription monitoring program three times in the past.

Not enough has changed to recommend that lawmakers change course.