Seattle police officers are warning heroin users about dangerous purity levels after four people overdosed on Saturday. Three of the overdoses were fatal.

The Seattle Police Department believes the victims may have bought heroin from the same person. All overdoses occurred within hours of each other and in a similar geographic area.

The SPD and King County health officials are urging users to take precautions.

If you’re going to use heroin, don’t use alone, they say.

“You'll die if you're alone. But if you have someone with you who's not using, who can monitor your health and reverse an overdose, call 911 immediately, hopefully you'll be able to survive,” said Jeff Duchin, health officer for Public Health Seattle and King County.