Can I overdose from my methadone dosage going up 20 mgs?

Yes. We understand how long most medicines stay in our bodies. However Methadone is different for each individual. Changing the dose of Methadone requires caution. The “half-life” of Methadone can very from 10 hours to 140 hours. An increase in Methadone for one person that is easily tolerated can be an overdose of another person.
Methadone 20mg. Yes you can overdose with any drug. The real issue is you are going yo to 20mg from what dose ?5mg, 10mg? If its too much of a jump then yes you could overdose. The rule should titrate up slowly to avoid complications and side effects.