The same law applies
RCW 46.61.502 makes it an offence to drive a vehicle while under the influence. It is not narrowed to cars, and a motorcycle is a vehicle.
The thresholds are the familiar ones: an alcohol concentration of 0.08 or higher within two hours of driving, or a THC concentration of 5.00 nanograms per millilitre of blood within two hours. You can also be convicted while under the influence of any drug, or a combination, without hitting a specific number.
The part that catches riders: the interlock
After a DUI, Washington requires an ignition interlock device on vehicles you operate, under RCW 46.20.720. There is no motorcycle exemption in that statute.
The practical problem is mechanical. An interlock requires a breath sample before starting and rolling retests while driving. That is designed around a car cabin. Most motorcycles cannot be fitted with one in any workable way.
The result is a rider who is technically permitted to drive an interlock-equipped vehicle but has no way to make their motorcycle compliant. In effect, riding stops for the duration.
It also blocks the endorsement itself
Separately, the DOL states plainly that you cannot add a motorcycle endorsement while an Ignition Interlock License is on your record. It has to be dropped first.
So a DUI does not merely restrict riding for existing riders. If you were partway through getting endorsed, that path is closed until the IIL is gone. Riders discover this at the counter, having already paid for and passed the training.
Why the physics are worse on two wheels
Setting the law aside for a moment. Riding is a balance task performed continuously, and alcohol degrades balance before it degrades almost anything else you would notice about yourself.
A car driver who is mildly impaired drifts within a lane. A rider who is mildly impaired makes late, coarse steering inputs and brakes badly, on a vehicle that requires precise ones and has no structure around it. Washington's own crash data lists riding under the influence among the leading rider-side contributing factors in fatal motorcycle crashes.
There is no version of this where the motorcycle is the more forgiving choice.
This is a guide, not legal advice
DUI law is genuinely complex, penalties escalate with priors, and the administrative licence consequences run on a separate track from the criminal case. If you are facing a charge, talk to a lawyer, not a training school. What we can tell you accurately is what it does to your endorsement.