What's happening
ADHD and replying to messages often goes wrong the moment you open one. Your mate asks how the new job's going, and you want to give a proper answer, not a rushed one, so you leave it for later. Once it's opened, the notification disappears and so does the reminder. A week on, it feels awkward to reply so late, so you leave it longer, and the guilt grows far bigger than the reply ever was.
How to get moving
If you can't reply properly right now, send a short holding message straight away, like "Saw this, will message you properly tonight". It takes ten seconds and takes the pressure off both of you. Then mark the chat as unread so it keeps nagging you. In WhatsApp, swipe right on the chat on an iPhone or press and hold it on Android, then choose Mark as unread. The other person will still see it as read.
In the iPhone Messages app, swipe right on a conversation to mark it unread. If typing a long reply is the bit you keep dodging, send a voice note while you're waiting for the kettle instead. For a message that needs to land at a set time, like good luck before an interview, you can write it now and schedule it with Send Later if you're using iMessage.
Important tip
Pick a regular reply slot, like the ten minutes after tea, and use it only to clear your unread chats, starting with the oldest. Keep each reply short. A two-line answer sent today does more for a friendship than a long one you keep meaning to write. If a reply is very late, "Sorry, this got buried" is enough. You don't need to write a full explanation before you get to the actual answer.
This is lived-experience content. It is not a promise that a particular idea will work for everybody.